This invention relates to a surgical resecting instrument whereby a cartilage (joint semicircle or joint cartilage), joint bump or tumor within such body cavity as a joint cavity, for example, of a knee is resected from outside the body cavity without incising it and is discharged out of the body cavity.
Conventionally, a joint has been operated on mostly by an incising method (open surgery). For example, in a general operation on a joint, a tumor on a knee skeleton is resected or a broken cartilage or bone is resected from a knee joint. Such operation has required a comparatively large incision. Therefore, there have been such defects that an external hurt will be produced by the incision, a pain and motion limitation will follow and much time will be required until the hurt is perfectly cured.
Therefore, there is recently suggested a surgical resecting instrument whereby, under the observation with a joint scope (endoscope), without incising a joint, a small stinging hole is formed in the joint and an insertable part is inserted into this stinging hole to operate on the joint. For example, in the publication of U.S. Pat No. 4,649,919, there is disclosed a surgical resecting instrument having an insertable part in which a rigid linearly extending inner tube provided at the tip with a cutting part is inserted through a rigid linearly extending outer tube. With this surgical resecting instrument, while a tissue is being bored with the tip of the inner tube, the tissue is shorn with a side opening near the tip. A blade for resecting this tissue is formed of an outer blade provided in the axial direction in a cylindrical outer tube and an inner blade (helcal cutter blade) rotatably inserted in the outer blade, having a fish tail-like cutting blade at the tip and provided on the side with a helical cutting blade.
Also, in German Utility Model No.8707238, there is disclosed a surgical resecting instrument wherein an inner blade having a helical blade at the tip is formed to be hollow and a sucking device is connected to this hollow part.
Now, in the above mentioned prior art, as the cutting blade on the side of the inner blade is formed to be helical, the shearing angle 8 in the case that the inner blade shears the tissue in cooperation with the opening of the outer blade has been constant as in FIG. 1.
Here, the shearing power P (in kg) is represented by the following formula: EQU P=t.sup.2 .tau./ (2 tan .theta.)
t : Thickness (in mm) of the shorn tissue. PA1 .tau.: Shearing resistance (in kg/mm.sup.2).
From the above formula, in case t and .tau. are constant, if the shearing angle .theta. is constant, the shearing power P will not fluctuate and such smooth shearing as is shown by the broken line in FIG. 2 will be made. However, in fact, as shown by the solid line in FIG. 2, the shearing power increases quickly at the beginning of the shearing stroke and then decreases to be constant in the course. When the shearing power thus quickly increases,the rotating speed will vary, the cutting efficiency will drop, a repeated stress will be applied to the cutting blade and therefore the blade will be likely to be fatigued and broken and will not be safe. Further, there is a problem that, when the side of the inner blade is formed to be a helical cutting blade, it will be difficult to work and expensive.